Method and apparatus for combusting fuel employing vortex stabilization

ABSTRACT

The present method and apparatus for producing a supersonic jet stream introduce an oxidizer in such a manner as to create a vortex, which is then restricted. Fuel is introduced into a reduced pressure eye of the vortex, forming a stratified composite stream of gases with unmixed oxidizer surrounding an inner mixture of fuel and oxidizer. This stratified composite stream is passed down a tube that exhausts to a low pressure environment. The combined fuel and oxidizer in the stratified stream is ignited to provide a high-velocity stream of combustion products. The outer layer of unmixed oxidizer in the vortex shields the tube and reduces or eliminates the need for additional cooling.

FIELD OF THE INVENTION

The present invention relates to a method and apparatus for combustingfuel with an oxidizer to obtain a high velocity jet of hot combustiongases, having particular utility for providing a thermal torch.

BACKGROUND OF THE INVENTION

In a classical combustion apparatus for producing a high-velocity flamejet, a fuel and an oxidizer are combined in a combustion chamber. Thecombined fuel and oxidizer are then ignited to produce combustion gases,and these gases are then accelerated through a nozzle. FIG. 1 is across-section view that illustrates a typical example of a conventionalcombustion device 10, having a housing 11 containing a combustionchamber 12. The combustion chamber 12 communicates with a nozzle 13 andan exit passage 14. An oxidizer, usually gaseous oxygen, is introducedinto the combustion chamber 12 through an oxidizer orifice 15. Fuel,either liquid or gas, enters the combustion chamber 12 through a fuelinlet 16 to mix with the oxidizer flow from the oxidizer orifice 15.Ignition, often provided by a spark-plug (not shown), occurs to form anintense flame in the combustion chamber 12. The width and length of thecombustion chamber 12 are sized to provide essentially completecombustion of the fuel and oxidizer. Prior to entry into the nozzle 13,the velocity of the hot combustion products is quite low. Thecombination of a restricting cross section of the nozzle 13 with anexpanding cross section of the exit passage 14 serves to greatlyaccelerate the combustion gasses. This structure is termed a de Lavalnozzle.

Due to the extreme heat generated in the combustion device 10, externalcooling is required. An outer shell structure 20 is spaced a smalldistance away from the housing 11, forming an annular coolant passage21. Water passes into the annular coolant passage 21 through a coolantinlet 22, exiting through a coolant outlet 23. The requirement for watercooling complicates the structure and reduces thermal efficiency, sincemuch of the energy generated by combustion is lost in the form of heat.

SUMMARY OF THE INVENTION

The method of the present invention for producing a supersonic jetstream includes the step of creating a vortex of an oxidizing fluidhaving an eye with a reduced pressure. The vortex is constricted andfuel is passed into the eye of the vortex to form a stratified compositestream, with unmixed oxidizer surrounding an inner mixture of fuel andoxidizer. This stratified composite stream is passed down a tube havinga bore that exhausts to a low pressure environment. The combined fueland oxidizer in the stratified stream are ignited to provide a stream ofcombustion products which can reach velocities exceeding the speed ofsound.

While the method has general applicability, it can be convenientlypracticed with a combustion and accelerator apparatus describedhereafter which constitutes part of the invention. In general, theapparatus is configured such that it merges and expands a fuel streamand an oxidizer stream and forms a vortex-stabilized composite streamhaving a fuel-rich core surrounded by an outer sheath of the oxidizer,with the combined fuel and oxidizer in the fuel-rich core providing anintermediate combustible mixture that, when ignited, expands to providea flame-stabilized high velocity jet.

The apparatus has a housing which terminates in a proximal end and adistal end. The housing has a cavity which is symmetrically disposedabout a central axis. The cavity has a central section which isgenerally cylindrical and nozzle section which extends to the distalend.

A fuel passage is provided in the housing and passes through theproximal end of the housing and into the cavity. The fuel passage is sopositioned such that it directs the fuel along the central axis.

A tube having a bore attaches to the housing at the distal end of thehousing, forming a continuation of the housing and terminating with afree end. The bore is symmetrically disposed about the central axis. Thelength of the tube is adjusted such that the oxidizer flow shrouds thewall of the tube extension along its entire length, assuring that itremains cool.

A fuel passage extender extends into the central section of the cavityand preferably terminates in the nozzle section or in the bore of thetube. It is preferred that the fuel passage extender be a taperedstructure having a cross section which, at least over a substantialportion of its length, reduces as a function of its distance from theproximal end of the housing.

The combustion apparatus is provided with a means for injecting theoxidizer into the central section of the cavity so as to create a vortexin the central section having a low pressure eye centered on the centralaxis. The nozzle section serves to constrict the vortex as it advancesthrough the housing.

This means for injecting the oxidizer can be provided by employing oneor more oxidizer passages that terminate in the central section of thecavity, each of the oxidizer passages being substantially tangent to acircle centered on the central axis and residing substantially in aplane normal to the central axis. By so introducing the oxidizer, avortex will be created in the central section of the cavity.

The vortex passes through the nozzle section and into the bore and, atsome point along this portion of the path, the fuel is released into theeye of the vortex in a manner such that the fuel remains directed alongthe central axis as it passes along the bore of the tube, thus providinga vortex-stabilized stratified fuel and oxidizer stream which remainsstratified as the oxidizer and fuel flow through the remainder of thestructure.

In some embodiments, the cross section of the bore increases as thedistance from the distal end of the housing increases. This increase canbe a continuous function of the distance or can be a stepwise increase.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a section view of a prior art combustion apparatus, which is achamber-stabilized torch suitable for depositing a layer of material ona target.

FIG. 2 is an isometric section view of a combustion apparatus that formsone embodiment of the present invention, which employs a single oxidizerinjection passage to provide a vortex-stabilized stratified fuel andoxidizer stream.

FIG. 3 is an exploded isometric view of the embodiment shown in FIG. 2,with a portion of a housing sectioned to better show the oxidizerinjection passage.

FIG. 4 is an enlarged cross section of the embodiment shown in FIGS. 2and 3 better showing the action of fuel and oxidizer within a tube whichforms part of the combustion apparatus shown in FIG. 2. The tube isillustrated with a schematic representation of a stratified stream offuel and oxidizer passing through and exiting a bore of the tube.

FIG. 5 is a cross section view of the combustion apparatus shown in FIG.4 after the composite stream in the tube has been ignited.

FIG. 6 is an isometric section view of a combustion apparatus which isfunctionally similar to that shown in FIGS. 2-5, but where the tube canbe readily replaced. The tube has an enlarged segment that slidablyengages a socket in a housing of the combustion apparatus, and aretention collar threadably engages the housing to secure the tube inthe socket.

FIG. 7 is an isometric section view of another combustion apparatus thatallows the tube to be readily replaced. In this embodiment, the housinghas a socket that is threaded and the tube has threads that engage thethreads of the socket to attach the tube to the housing. An alternativetube having a smaller bore is also illustrated, which can beinterchanged with the first tube to allow the bore size to be varied tosuit the desired operating parameters for the combustion apparatus.

FIGS. 8 and 9 are section views that schematically illustrate one methodfor experimentally determining an appropriate length of a tube for acombustion apparatus such as those shown in FIGS. 2-7. In this method, atube blank that is longer than the anticipated tube length is employedand is operated in a combustion apparatus under the desired operatingconditions. The tube blank melts off at a point which indicates themaximum practical length, and the tube is then made somewhat shorterthan this maximum practical length.

FIG. 10 is a partially exploded isometric view of a combustion apparatusthat forms another embodiment of the present invention, where thehousing and the extension are formed as an integral unit and theoxidizer is preheated by passing it through the wall of the extension.In this embodiment, the oxidizer is injected into a central section of acavity via a plurality of oxidizer passages that communicate between anoxidizer manifold and the central section. The tube of this embodimenthas a bore with a stepped profile so as to enhance the acceleration ofthe combusting gases and reduce noise.

FIG. 11 is a sectioned view of the embodiment shown in FIG. 10 whenassembled.

FIG. 12 is a section view of another embodiment, which is similar tothat shown in FIGS. 2-5 but where a water-cooling jacket is providedaround the tube to allow the use of a longer tube.

FIG. 13 is a section view of another embodiment that uses water cooling,but where the water is introduced into the vortex of uncombinedoxidizer.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 2 illustrates one embodiment of the present invention, a combustionapparatus 30. FIG. 3 shows an exploded view of the same embodiment. Thiscombustion apparatus 30 can be fabricated from three pieces of stock. Atube 32 is attached to a body section 34 which in turn attaches to abacking section 36. The backing section 36 in turn has a fuel coupling37 for connection to a conventional fuel supply line (not shown). Thetube 32 is preferably of high conductivity copper to provide greaterheat transfer, while the body section 34 and the backing section 36 canbe formed of brass. The body section 34 also attaches to an oxidizercoupling 38 for connection to a conventional oxidizer supply line (notshown).

While the structure of the combustion apparatus 30 can be defined interms of the pieces from which it can be fabricated, it is moreconvenient to discuss the structure in terms of the functional elementswhich provide certain functions on the oxidizer stream and the fuelstream as they pass through the combustion apparatus 30.

The combustion apparatus 30 has a housing 40 that terminates at aproximal end 42 and a distal end 44. The housing 40 has a cavity 46symmetrically disposed about a central axis 48. The cavity 46 isterminated in part by the proximal end 42, defined by the backingsection 36 which has a central fuel injection passage 50 therethroughwhich communicates with the fuel coupling 37. The fuel injection passage50 has a fuel passage axis 52 which coincides with the central axis 48.The backing section 36 is provided with a fuel passage extension 53which continues the fuel injection passage 50 into the cavity 46. Thecavity 46 has two sections, a central section 54 which is generallycylindrical, being radially terminated by a peripheral wall 56 that is acylindrical surface symmetrically disposed about the central axis 48,and a nozzle section 58 which connects the central section 54 to thedistal end 44.

An oxidizer injection passage 60 is provided to inject an oxidizer fromthe oxidizer coupling 38 into the central section 54 of the cavity 46.The oxidizer injection passage 60 is configured to direct the oxidizerinto the central section 54 in a tangential manner so as to generate avortex centered on the central axis 48, the vortex subsequently passingthrough the nozzle section 58 and into a bore 62 of the tube 32.

The bore 62 of the tube 32 is symmetrical about a bore axis 64, and thetube 32 is attached to the housing 40 such that the bore axis 64 alignswith the central axis 48 of the cavity 46 and with the fuel passage axis52. The joinder of the tube 32 with the housing 40 can be made by avariety of techniques. As depicted in FIGS. 2 and 3, the housing 40 ofthis embodiment is provided with an opening 65 in the distal end 44which slidably accepts an insertable section 66 of the tube 32. Theinsertable section 66 of the tube 32 has the bore 62 reshaped over theregion thereof that is adjacent to the central section 54 of the cavity46 when the tube 32 is properly inserted into the opening 65, thisshaping of the bore 62 forming the nozzle section 58 of the cavity 46.The tube 32 in this embodiment is secured to the housing 40 by solderingor other appropriate joining technique.

FIGS. 4 and 5 are sectional side views of the combustion apparatus 30shown in FIGS. 2 and 3, to better illustrate one preferred spacialrelationship between the fuel passage extension 53 and the bore 62 ofthe tube 32. In this embodiment the fuel passage extension 53 continuesbeyond the nozzle section 58 into the bore 62. FIG. 4 illustrates thecombustion apparatus 30 in an initial startup condition where theoxidizer is being provided to the combustion apparatus 30 and hasestablished a vortex, schematically represented by 70, having a lowpressure core 72 or eye of the vortex 70 which is centered on the boreaxis 64.

FIG. 5 illustrates the combustion apparatus 30 after fuel is beingdirected into the low pressure core 72 and is ignited to form acombustion region 74 that increases in cross section as the fuel passesdown the bore 62. The limit of the expansion will be determined by thelength of the tube 32, and should be maintained such that an unmixedsheath region 76 of the oxidizer surrounds the combustion region 74throughout the length of the bore 62 to buffer the tube 32 from the heatgenerated by the combustion and to enhance the efficiency of thecombustion apparatus 30, since loss of thermal energy is reduced. Havingthe combustion apparatus 30 so operated results in greater accelerationof the combustion products. In fact, the output from combustionapparatus 30 exhibits shock diamonds 78, indicating that the outputstream has reached supersonic flow. The unmixed sheath region 76 resultsfrom operating the combustion apparatus 30 in such a manner that theradial advancement of flame in the combustion region 74 as it passesthrough the bore 62 is greater than the rate of diffusion of theunburned fuel radially outward into the oxidizer. It should be notedthat the formation of the low pressure core 72 allows the combined fueland oxidizer to be ignited after exiting the bore 62, in which case theflame rapidly progresses upstream to form the combustion region 74within the bore 62. Alternatively, the combined fuel and oxidizer couldbe ignited within the bore 62, such as by a spark plug (not shown).

FIGS. 6 and 7 each illustrate an alternative embodiments of combustionapparatus (30′ and 30″, respectively) which each has a replaceable tube(32′ and 32″), but which is each functionally the same as the combustionapparatus 30 discussed above and shown in FIGS. 2-5. In the case of thecombustion apparatus 30′ shown in FIG. 6, the tube 32′ fits into asocket 80 which extends the distal end 44′ of the housing 40′. Aretention collar 82 threadably engages the distal end 44′ and forciblyengages an enlarged segment 84 of the tube 32′ to lock the tube 32′ inthe socket 80.

In the combustion apparatus 30″ shown in FIG. 7, the tube 32″ threadsdirectly into the socket 80′ of the housing 40″. FIG. 7 also illustratesan alternate tube 32′″ that could be exchanged for the tube 32″ toprovide a smaller bore 62′.

FIGS. 8 and 9 illustrate an experimental approach for determining anappropriate length L of a tube 90 for a combustion apparatus 92 having astructure similar to that of the combustion apparatus 30 discussedabove. The combustion apparatus 92 also has a housing 94 to which thetube 90 is affixed. For a particular set of operating parameters, amaximum practical length L_(MAX) for the tube 90 can be determinedexperimentally. To do this, a tube blank 90′ having an initial lengthL_(I) which is substantially longer than the final length L is attachedto the housing 94 and fuel and oxidizer are introduced into thecombustion apparatus 92 according to the desired operating parameters.When the combined fuel and oxidizer is ignited and burns, the combustiongases expand as they progress down the tube blank 90′, and at some pointexpand so as to be close enough to the tube blank 90′ that the sheath ofcool oxidizer is no longer sufficient to prevent substantial heating ofthe tube blank 90′. At some point along the length of the tube blank90′, indicated by the line A-A, the heat from the combustion gasescauses a terminal portion 96 (shown in phantom) of the tube blank 90′extending beyond the line A-A to melt, leaving a base portion 98 of thetube blank 90′ remaining. The length of the base portion 98 extending tothe line A-A defines the maximum practical length L_(MAX) for theparticular operating conditions employed. The length L of the tube 90 isthen selected to be somewhat shorter than the maximum practical lengthL_(MAX).

While all the embodiments discussed above have a single oxidizer passagefor introduction of the oxidizer into the cavity so as to form a vortexthat travels through the chamber, in some instances it is preferred toemploy multiple passages to introduce the oxidizer into the chamber. Insuch cases, it is frequently advantageous to provide an annular manifoldfor the oxidizer, this manifold encircling the at least a portion of thecavity and serving as the connector between the oxidizer source and thepassages. FIGS. 10 and 11 illustrate a combustion apparatus 100 thatforms one embodiment of the present invention that employs such anoxidizer manifold.

The combustion apparatus 100 again is designed to swirl the oxidizer asit is introduced; however, in this embodiment the oxidizer is introducedinto the cavity through multiple passages. The combustion apparatus 100has a structure with only three parts, each of which is designed to bereadily fabricated by machining.

The combustion apparatus 100 has a main body 102 and a proximal body 104which, in combination, form a housing with a cavity 106. In thisembodiment, the cavity 106 is surrounded by an oxidizer manifold 108.The main body 102 also serves as a tube, having a bore 110 therethroughwhich communicates with the cavity 106. The main body 102 and theproximal body 104 are attached together at a single body joint 112,which can be sealed by soldering to seal the oxidizer manifold 108.While there is no sealed joint between the cavity 106 and the oxidizermanifold 108, the effect of any oxidizer leakage through this jointshould be negligible.

The oxidizer manifold 108 introduces oxidizer into a central section 113of the cavity 106 via a series of tangentially-directed oxidizerpassages 114 passing through a wall 116 that defines the periphery ofthe central section 113, forming a vortex that is then constricted bypassing through a nozzle 117.

The oxidizer is introduced into the oxidizer manifold 108 from anoxidizer inlet 118 through a series of passages which run alongside thebore 110. The oxidizer inlet 118 can connect to an oxidizer couplingsuch as that shown in FIGS. 2 and 3. From the oxidizer inlet 118, theoxidizer is first passed forward by a forward conduit 120 to a forwardannular space 122. The forward annular space 122 is formed by a forwardring 124 that is sealably attached to the main body 102 at two forwardring joints 126; again, these joints 126 can be soldered. The forwardannular space 122 circumscribes the bore 110.

From the forward annular space 122, the oxidizer is passed rearward tothe oxidizer manifold 108 through a number of side conduits 128 thatextend through the main body 102 parallel to the bore 110. The sideconduits 128 communicate between the forward annular space 122 and theoxidizer manifold 108.

In the combustion apparatus 100, the bore 110 expands in cross sectionas the distance from the cavity 106 increases. Such could be provided bya gradually expanding cross section; however, for ease of machining theembodiment illustrated, the bore 110 is expanded by forming a series ofbore cylindrical sections 130, where the diameter of each of the borecylindrical sections 130 increases as the distance of the borecylindrical section 130 from the cavity 106 increases.

When the combustion apparatus 100 is to be employed to apply a coating,means are provided for introducing a coating material into the stream ofcombustion gases. In the embodiment illustrated, such means are providedby a wire-guiding passage 132 extending through the main body 102. Thewire-guiding passage 132 is inclined with respect to a central axis 134,about which the cavity 106 and the bore 110 are symmetrically disposed.The wire-guiding passage serves to direct a wire (not shown) passedtherethrough such that the wire will intersect the stream of combustiongases exiting from the bore 110. The hot combustion gases can then meltthe end of the wire to introduce molten droplets of the coating materialinto the stream of gases, which then accelerates these droplets toimpact against a workpiece to be coated.

An alternative approach to introducing a coating material would be tointroduce a powder into the stream of fuel which is introduced into thecavity 106 through a fuel passage 136 that extends through the proximalbody 104 and is aligned with the central axis 134. In the combustionapparatus 100, introducing powder into the oxidizer stream would beimpractical in view of the number of passages and spaces (120, 122, 128,108, and 114) through which the oxidizer passes before reaching thecavity 106. In any case, it is preferred for the fuel passage 136 to beextended into the cavity 106 by a fuel passage extender 138.

The above examples have been for combustion apparatus embodiments thatdo not employ water cooling, and hence limit the length of the tube inwhich the combustion occurs to assure that a layer of unmixed oxidizerresides against the tube along its length, this layer serving to protectthe tube from the heat of the combustion gasses. The length of the tubecan be increased if the tube is water-cooled. The water cooling can beaccomplished by employing a water jacket and/or by injecting water intothe vortex of the oxidizer, as discussed below.

FIG. 12 illustrates a combustion apparatus 200 which has a housing 202and a tube 204 attached thereto. The tube 204 is encased in a watercooling jacket 206 which provides an annular water passage 208 aroundthe tube 204. The jacket 206 is provided with a water inlet 210, intowhich cooling water is introduced, and a water outlet 212 where thewater exits the jacket 206. The water is heated as it passes along aterminal portion 214 of the tube 204, the terminal portion 214 being theportion which is beyond a self-cooling section 216 of the tube 204 wherethe tube 204 is cooled by the oxidizer. Thus, the heat input that isextracted by the water is substantially less than the heat extracted bywater jacket of the prior art, since much of the tube 204 is shielded bythe vortex of the oxidizer, and therefore most of the heat generated bythe burning remains in the combustion products as they pass down thetube 204.

FIG. 13 illustrates another combustion apparatus 300 which has a housing302 and a tube 304 attached thereto. In this embodiment, a water inlet306 is provided which allows water to be injected into a vortex that isformed by the oxidizer as it passes down the tube 304. The waterintroduced into the vortex is spun to a bore surface 308 of the tube304, since the water is more dense than that oxidizer; this spun waterforms a water film 310 on the bore surface 308. As the combustionproducts expand radially, the oxidizer is exhausted and the water film310 initially provides shielding over the additional length and, forthis additional length, provides shielding of the tube 304. By adjustingthe flow of the water into the tube 304, one can adjust the water flowsuch that a dry output will be provided without overheating of the tube304. This technique has an additional benefit in that it changes thecharacter of the output combustion products and maintains a lessoxidizing output. In fact, one can obtain the desired flow by monitoringthe color of the output of the torch while adjusting the input waterflow.

While the novel features of the present invention have been described interms of particular embodiments and preferred applications, it should beappreciated by one skilled in the art that substitution of materials andmodification of details can be made without departing from the spirit ofthe invention.

1-10. (canceled)
 11. A method for producing a supersonic jet stream,comprising the steps of creating a vortex of an oxidizer within andthrough a constricting bore, the vortex having a low pressure eyeaxially positioned within the bore; passing a fuel into the eye of thecontinuously constricted vortex flow to form a stratified compositestream: passing the vortex and stratified composite stream through andout of said constricting bore; igniting the stratified composite stream;and, limiting the length of said constricting bore to that length whichmaintains an annular sheath of cold oxidizer completely surrounding theexiting flame jet to prevent over-heating the material containing saidbore. 12-20. (canceled)